1. Field of the invention
The present invention relates to a hydraulic control valve employed, for example, in a hydraulic brake system of a vehicle and capable of relieving the pressure when the same is excessive.
2. Description of the Prior Art
Such a hydraulic control valve is designated generally as a proportional valve. Known hydraulic control valves are disclosed in Japanese Unexamined Patent Publication Nos. 59-50844 and 59-50846 which were published in Japan in 1984.
Hydraulic control valves may employed, for example, in automotive hydraulic brake systems. Such a hydraulic control valve is provided in a hydraulic line between the master cylinder and the rear wheel cylinder. When a fluid pressure exceeding a predetermined level is applied to the rear wheel cylinder during the operation of the brake system, the hydraulic control valve relieves the pressure working on the rear wheel cylinder so that the front and rear wheels are braked at an appropriate braking ratio.
When a vehicle is equipped with a traction control system or an antiskid control system to prevent the driving wheels from slipping during acceleration or braking, the hydraulic brake circuit is provided with a cutoff valve to control the hydraulic circuit in addition to the proportional hydraulic control valve.
However, providing the hydraulic circuit with those two valves complicates the hydraulic circuit, requires a large space for the hydraulic circuit and enhances the weight of the hydraulic circuit.